"Our study suggested that improved oral hygiene may be associated with a decreased risk of new-onset diabetes," said study author Dr. Yoonkyung Chang. She is a clinical assistant professor of neurology at Ewha Woman's University Mokdong Hospital, in South Korea.

Chang said the researchers don't know what the exact mechanism behind this connection is, but there are a number of possible ways that poor dental health might contribute to diabetes.

"Poor oral hygiene may be related to the chronic inflammatory process," she said. Inflammation affects oral health and can lead to gum disease that creates space in the gum where bacteria can collect. That bacteria may then travel into the body's circulation and trigger immune system responses, which might impair blood sugar control.

But it's difficult to prove a cause-and-effect relationship between dental health and diabetes because many factors involved in poor oral health are also linked to type 2 diabetes.

Endocrinologist Dr. Akankasha Goyal, from NYU Langone Health in New York City, wasn't involved in the research, but is familiar with the findings.

"We don't know if having poor dental health can cause diabetes, but we do know the other way is true: Diabetes can cause poor dental health," she said.

The higher blood sugar levels that can occur in diabetes can lead to cavities and poor dental health. Plus, she said many of the same dietary factors -- such as eating highly processed carbohydrates -- are associated with both poor dental health and diabetes, making it harder to know which comes first.

The study looked at data from almost 190,000 people in South Korea. Their average age was 53. The information was collected between 2003 and 2006. About one in six people had gum disease at that time.

The average follow-up time was 10 years. During that time, about 16% of the study group developed diabetes.

The researchers used computer modeling and controlled the data for a number of factors, including age, weight, blood pressure, physical activity, income, smoking status and alcohol consumption.

The investigators found that having gum disease was linked to a 9% increase in the risk of diabetes. People who were missing 15 or more teeth had a 21% higher risk of diabetes.

On the other hand, good oral health was associated with a lower risk of diabetes. People who brushed their teeth three or more times a day had an 8% lower risk of diabetes.

The effect of good oral hygiene and reduced diabetes risk seemed stronger for younger people (51 and under). Brushing often also appeared to offer more protection against diabetes for women, though the study authors noted that the reasons why are unclear.

Goyal said good oral hygiene is important for everyone. "Floss and brush at least twice a day," she said.

For people who already have diabetes, it's important to get a dental checkup at least once a year, though Goyal noted the dentist will likely advise at least twice a year.

For people who don't have diabetes, a healthy lifestyle can help prevent type 2 diabetes. "Portion control is important. Eat multiple small meals throughout the day. Participate in regular activity -- at least 150 minutes a week. And stop smoking," Goyal advised.